lvm resizing and shifting

[Roberto Ragusa]

Craig White wrote:
> I was able to reduce the size of the logical volumes, move the logical
> volumes so they are adjacent and then reduce the size of the physical
> LVM but I cannot seem to reduce the partition itself and I'm gathering
> that this may not be possible.
> 
> # pvdisplay
>   --- Physical volume ---
>   PV Name               /dev/sda2
>   VG Name               VolGroup00
>   PV Size               95.00 GB / not usable 31.81 MB
>   Allocatable           yes
>   PE Size (KByte)       32768
>   Total PE              3039
>   Free PE               127
>   Allocated PE          2912
>   PV UUID               oAYcCQ-5n28-0C6i-1LLE-voCR-E19v-SQYQK0
> 
> # fdisk -l /dev/sda
> 
> Disk /dev/sda: 203.9 GB, 203928109056 bytes
> 255 heads, 63 sectors/track, 24792 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Disk identifier: 0x00086350
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sda1   *           1          13      104391   83  Linux
> /dev/sda2              14       24792   199037317+  8e  Linux LVM
> 
> # df -h
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/root              88G   54G   30G  65% /
> /dev/sda1              99M   36M   59M  39% /boot
> 
> so in the end, /dev/sda2 remains approximately 200G and even the
> gpartd-liveCD cannot resize /dev/sda2   ;-(
> 
> Is it even possible?

What you are attempting is not a common way to use the LVM system.
I often create many pv on one disk (sda2, sda3, sda4) just to avoid
this kind of problems.

The pv is now 95G, so only the first 95G of sda2 are used (usable).
Now, thinking about it, resizing sda2 could simply mean you
have to delete and immediately recreate sda2 with a smaller size.
We just have to be sure about where the pv metadata are stored.
According to

   http://www.guug.de/lokal/rhein-main/2004-09-23/LVM2_sage_23.09.pdf

we learn that

   LVM2 format is an ASCII text format which is at the beginning,
  after a disk label, of every PV in 2 copies by default
   in large configurations...

so it is at the beginning of the pv.

The procedure I'd try (assuming I had a backup of everything, as
_this is obviously dangerous_):

1) Boot from CD and without any kind of lvm detection.
2) Destroy sda2 and recreate it as 100G.
3) Boot the system again, check that the LVM is OK and
pvresize sda2 in automatic size (so it goes from 95G to 100G).

Step 3) avoids that you have to calculate the new size for sda2,
which is very difficult because of the partition and LVM roundings.

If you find the courage to try this, let me know how it went.

:-)


-- 
    Roberto Ragusa    mail at robertoragusa.it